In one of the worst accidents in Indian Naval history, a major blast ripped through the Sindhurakshak - a kilo class submarine that had undergone a major refit at Russia's Zvezdochka shipyard - at the Naval Dockyard in Mumbai, sending it to the bottom with 18 crew members on board.
All the crew, including three officers, are now feared dead.
According to TV reports, the blast ripped through Sindhurakshak a few minutes past midnight on Wednesday. The submarine has sunk with only a portion of it visible.
Naval divers launched a despairing search for survivors but were unable to enter the submarine as its hatches are crumpled.
INS Sindhurakshak was fully armed at the time of the accident. As a result, when the fire spread to the forward portion, which contains the torpedoes, it set off several devastating explosions, which hit another submarine INS Sindhuratna.
However, the damage to INS Sindhuratna is minor.
At least 16 fire tenders from the Naval Dockyard as well as Mumbai city along with a team of Naval experts are carrying out the rescue operations.
INS Sindhurakshak was 15 to 20 metres away from the jetty in the sea when the incident took place.
A Board of Inquiry is being instituted to investigate into the causes of the accident.
Defence minister A K Antony is to visit the Mumbai naval dockyard today. He is also expected to make a statement in Parliament on the issue, on which reports say he has briefed Prime Minister Manmohan Singh.
The opposition Bharatiya Janata Party has demanded a statement in Parliament, but has been told that this will only be possible after Antony returns from Mumbai.
Speaking to the media Antony said that he was very sorry for the people who lost their lives.
This is not the first time that INS Sindhurakshak has encountered a problem. The submarine, which was on its way to India after delivery by Russia in January 2013, ran into rough weather near Egypt.
A distress call in May 2013 had then seen the Egyptian Navy tow the submarine to its dockyard, where repairs had to be undertaken.
Armed with its latest multi-role missile system, radar and electronics, the submarine was to be the backbone of the Indian Navy.
The submarine had undergone a $80-million refit that saw the submarine's hull being overhauled, installation of upgraded electronic warfare and weapons control systems, mounting of Indian-made sonar USHUS and radio communication systems.
Naval experts believed the submarine could have acted as a game-changer because it was fitted with the Club-S multi-role missile system capable of eliminating targets at a distance of over 250 km.
INS Sindhurakshak, a Type 877EKM in Russia, was constructed at St Petersburg in 1997. The submarine was designed to patrol and to protect naval communications, assault warships, enemy submarines, land targets and perform naval reconnaissance.
Navy chief Admiral D K Joshi has arrived at the naval dockyard in Mumbai to study the situation.